Is presenting patients with moral reminders prior to psychological testing a fruitful deterrence strategy for symptom over-reporting? We addressed this question in three ways. In study 1, we presented individuals seeking treatment for ADHD complaints (n = 24) with moral primes using the Mother Teresa Questionnaire and compared their scores on an index of symptom over-reporting (i.e., the Structured Inventory of Malingered Symptomatology, SIMS) with those of unprimed patient controls (n = 27). Moral primes slightly decreased SIMS scores, but the effect was not significant. In study 2, we took a different approach to activate moral categories: we recruited individuals seeking treatment for ADHD complaints and asked some of them to sign a moral contract (i.e., prime; n = 19) declaring that they would complete the tests in an honest way and compared their scores on the SIMS and standard clinical scales measuring self-reported psychopathology with those of unprimed patient controls (n = 17). Again, we found no convincing evidence that moral cues suppress symptom over-reporting. In study 3, we gave individuals from the general population (N = 132) positive, negative, or neutral moral primes and implicitly induced them to feign symptoms, after which they completed a brief validated version of the SIMS and an adapted version of the b Test (i.e., an underperformance measure). Again, primes did not affect over-reporting tendencies. Taken together, our findings illustrate that moral reminders are not going to be useful in clinical practice. Rather, they point towards the importance of studying contextual and individual difference factors that guide moral decision-making in patients and may be modified to discourage symptom over-reporting.